Position-indicating apparatus and ignition system employing same



Nov. 30, 1965 J, c m 3,221,213

POSITION-INDICATING APPARATUS AND IGNITION SYSTEM EMPLOYING SAME FiledApril 11, 1963 I sPAhK PLUG-S L J J mm'oT-vmm? 5:535? D GENERATINGCIRCUITRY ASSEMBLY PIC-3.2.

INVENTDR'. dOl/N R. M K/NNEV .er WA United States Patent 3,221,213POSITION-INDICATENG APPARATUS AND HGNITION SYSTEM EMPLOYING SAME John R.McKinney, 111 Brittany Drive, Chalfont, Pa. Fiied Apr. 11, 1963, Ser.No. 272,343 Claims. (Cl. 315-209) This invention relates to apparatusfor producing electrical indications of the position of an adjacentobject, and particularly to apparatus suitable for use in an ignitionsystem to produce electrical pulses synchronized with rotation of anobject such as the cam shaft of an internal combustion engine. Theinvention also relates to apparatus for sensing the strength of amagnetic field.

Ignition systems for internal combustion engines are known in whichpulses of high voltage are applied to ignition-producing spark plugs intimed relation to the occurrence of the combustion phase of the enginecycle in each cylinder. For this purpose there are commonly employed anelectrical circuit for producing pulses of high voltage, a distributorwith rotor for applying the high-voltage pulses in sequence to thevarious cylinders when the engine employs more than one cylinder, andbreaker-switch apparatus opened and closed by a camming arrangementsynchronized with rotation of the cam shaft, the breaker-switchapparatus being connected to the electrical circuit producing thehigh-voltage pulses so as to control the times at which such pulses aregenerated, in well known manner. Typically the breakerswitch apparatusis opened and closed by the pressure of camming surfaces located on ashaft driving the distributor rotor, to open and close directly acircuit through the primary of an ignition coil. More recently it hasbeen proposed to use opening and closing of the breakerswitch apparatusto turn on and off a power transistor having its emitter-to-collectorpath in series with the ignition-coil primary, thereby reducing thecurrent and voltage which the breaker points must withstand andgenerally obviating the necessity for use of a condenser across thebreaker points.

While such ignition systems using breaker-switch apparatus have beenused commercially for many years, they possess the inherent drawbackthat the timing, and in many cases the magnitude, of the high-voltagepulses is affected by unavoidable wear between the camming surfaces andthe breaker-switch apparatus, as well as by wear and electricaldeterioration and pitting of the breaker-switch points. In addition,because mechanical opening and closing of physical switch elements isemployed, it is ditiicult to operate the breaker-switch apparatus withsufficiently accurate timing at the high rates associated with highengine speeds, and therefore the engine power potentially achievable athigh engine speeds is not fully realized in most cases. For these andother reasons it has been recognized that it would be desirable toeliminate the breaker-switch apparatus entirely from such engines.

Proposals have been made to eliminate the breakerswitch apparatus byreplacing it with a piezoelectric element having mechanical meansassociated therewith, cammed or geared to the engine cam shaft, forshocking or stressing the piezoelectric element to cause it to generatevoltage pulses for controlling the times of occurrence of ignitionpulses. However, moving physical contacts, productive of wear adverselyaffecting the timing and/ or magnitude of ignition pulses, are againemployed.

Similar problems arise in other situations in which it is desired toproduce electrical pulses synchronized with motion of a physical object,particularly where an accurately-timed electrical pulse is to beproduced Whenever a rotating object attains a predetermined angularposition.

Patented Nov. 30, 1965 Accordingly it is an object of my invention toprovide new and improved apparatus for sensing and providing electricalindications of the position of a physical object, and particularly ofits angular position.

Another object is to provide such apparatus which does not requirephysical contact between the object whose position is sensed and theapparatus for sensing it.

A further object is to provide new and improved apparatus for producingelectrical pulses in timed synchronization with the attainment by arotating member of predetermined angular positions.

Another object is to provide apparatus for producing an electrical pulseeach time a piston or vane of an internal combustion engine reaches aposition for which an ignition spark is desired, without requiring theuse of breaker-switch apparatus.

It is a further object to provide apparatus of the lastmentioned typewhich is capable of accurate and reliable operation at high enginespeeds, which exhibits a minimum of deterioration in performance uponlongcontinued operation, and which is compatible with, and suitable forsubstitution in, existing types of ignition systems.

It is also an object to provide a new and improved device for sensingthe strength of a magnetic field.

These and other objects of the invention are achieved by the provisionof apparatus comprising a piezoelectric element, a body of magneticmaterial joined to said element, and means, at least a portion of whichis of magnetic material and movable with respect to said element throughpositions adjacent but spaced from said body of magnetic material, forvarying the magnetic field acting on said body to produce diiferentforces between said body and said element for predetermined dilferentpositions of said means, thereby to change the stresses on saidpiezoelectric element and to cause said elementto generate electricalvoltages of a magnitude dependent on the contemporaneous position ofsaid means.

For example, in a preferred form of the invention as applied to internalcombustion engines, a piezoelectric element having a magnetic materialthereon is positioned so that, as the rotor of the distributor of aninternal combustion engine turns through each of a plurality ofpredetermined, discrete, angular positions for which ignition of sparkplugs is to be produced, a changing magnetic force acts on the magneticmaterial and changes markedly the pressure between the piezoelectricelement and the magnetic body thereon, in turn causing the piezoelectricelement to generate a marked voltage change, or pulse, each time one ofsaid angular positions is reached. These voltage pulses may then be usedto actuate a highvoltage generating ignition circuit, preferably atransistorized circuit, to cause the circuit to generate highvoltageignition pulses for application to the spark plugs at the optimum timesfor ignition of the combustible gas in the engine cylinders.

In this system the use of contact-actuated devices such as breakerswitches is eliminated, and accordingly this source of deterioration ofperformance due to wear is eliminated, and the accuracy and consistencyof performance at high engine speeds greatly enhanced. Unlike variousother piezoelectric ignition systems which have been proposed, there isno wear and no failure at high speeds due to mechanical coupling to thepiezoelectric element, and the relatively gentle and reproducible forcesexerted on the piezoelectric element in the system of my inventionconduce to long and reliable life of the element and to the generationof a voltage pulse of reproducible waveform well suited for the purposeof ignition voltage control.

These and other objects and features of the invention will be morereadily comprehended from a consideration of the following detaileddescription in connection with the accompanying drawings, in which:

FIGURE 1 is a representation, partly in perspective and partlyschematic, showng one type of ignition system for an internal combustionengine to which the invention is applicable;

FIGURE 2 is an elevational view, partly in section and partly brokenaway, of a part of the system of FIGURE 1 showing in detail one form ofangular-position indicating apparatus in accordance with the invention;

FIGURE 3 is a top view of a portion of the angularposition indicatingapparatus of FIGURE 2; and

FIGURE 4 is an enlarged fragmentary view in perspective of a part ofsaid angular-position indicating apparatus.

Referring now to the specific embodiment of the invention illustrated inthe figures by way of example only, FIGURE 1 illustrates an ignitionsystem for an internal combustion engine such as a four-cylinderautomobile engine (not shown), comprising ignition-voltage genera ingcircuitry for developing and for applying highvoltage pulses by way ofcable 11 to a distributor and timing assembly 12, which contains theusual voltage-distributing arrangement for supplying the high-voltagepulses in sequence to four spark plugs 14, 16, 18 and 20 by way ofcables 22, 24, 26 and 28 respectively. The distributor and timingassembly 12 also includes means in accordance with the invention forproducing relatively small-amplitude electrical control pulses and forsupplying them by way of cables 32 and 34 to the circuitry 10 to controlthe times at which high-voltage pulses are generated therein so thatthey will occur at phases of the cycle of the engine which are optimumfor gas ignition in the engine cylinders. It is understood that a rotorshaft 35 is connected in conventional manner to rotate in synchronismwith the engine cam shaft, and that high-voltage pulses are therefore tobe generated at four predetermined, equi-spaced, angular positions ofthe rotor shaft 35.

The ignition-voltage generating circuitry 10 for responding to eachrelatively-small amplitude control pulse supplied thereto from cables 32and 34 to produce a corresponding high-voltage pulse at cable 11 may beof any of a large variety of forms which will readily occur to oneskilled in the art. For the present purpose it is preferred andadvantageous to employ a transistorized circuit, which may be of thetype shown in which the secondary 36 of a voltage step-up transformer 38has its primary 40 connected in series with a battery 42, an ignitionswitch 44, a current-limiting resistor and the emitter-to-collectorcurrent path of a power transistor 46. The polarity of the battery issuch that when the transistor is turned on by an appropriate voltagebetween its base and emitter, an intense current flows through thetransformer primary 40, and when the transistor is turned off theprimary current ceases abruptly. In the example shown the transistor 46is of the PNP type and its collector and the positive terminal ofbattery 42 are grounded, for example to the engine block, so thatnegative control voltages at the transistor base turn on the transistorand positive voltages turn it off. Ernitter-to-base bias is provided bythe two resistors and 52 connected in series between collector andemitter, the base being connected to the interconnection of theresistors. By suitably proportioning the values of the resistors 50 and52 the transistor 46 may be biased normally on and turned offmomentarily by a positive control pulse from cable 32, or may be biasednormally off and turned on momentarily by a negative control pulse. Forthe present example it will be assumed that the former biasingarrangement is used. In this case, when ignition switch 44 is closedcurrent flows through the primary 40 of ignition coil 38 until theengine turns rotor shaft 35 through a position for which a positivecontrol pulse is applied to cable 32 at which time current throughprimary 4%] ceases suddenly and a high-voltage amplified many times withrespect to the control pulse is produced across the secondary $6 forapplication to the spark plugs.

As mentioned earlier, the exact form of the ignitionvoltage generatingcircuitry 10 is not critical to the invention in its broader aspects,and the particular circuit shown has been chosen primarily forsimplicity and clarity of exposition. It will be understood, forexample, that ordinary diodes and/or zener diodes may be connected atthe input to the transistor to limit the amplitude of applied controlpulses or to eliminate control pulses of polarity opposite to thedesired one, that a plurality of transistors or of other devices such asvacuum tubes may be used for increased gain and stability, and that anyof a variety of types and connections of ignition coil may be used. Insome cases it will be desirable to include a D.C.-'olocking capacitorbetween cable 32 and the interconnection of resistors 59 and 52. Inaddition it will be understood that other conventional elements, such asthe generator and starter circuits (not shown) for the engine, may beappropriately connected into the circuit in known manner.

Considering now the arrangement for producing control pulses acrosscables 32 and 34 in accordance with the invention, with particularreference to the view of distributor and timer assembly 12 shown inFIGURE 2, a conventional housing of insulating material having a lowerportion 50 and a removable cap portion 52 is mounted with rotor shaft 35extending concentrically therein, the arrangement being such that therotor is free to rotate with respect to the housing. The upper end ofthe rotor shaft carries the usual insulating rotor arm 56 with itsdistributor contact 57, high-voltage pulses from cable 11 beingdistributed in sequence to the various spark plug cables by way of rotorcontact pin 58 and distributor contact 57 as the rotor shaft turns insynchronism with the engine cam shaft.

The lower portion Stl of the housing supports a mounting plate 59 havinga central aperture to clear the rotor shaft 35. A suporting block 69 ofan electrically-conductive non-magnetic material such as aluminum ismounted in fixed position on plate 59, preferably electrically insulatedtherefrom by an insulating layer 61. Mounted rigidly to the top of block69 in cantilever fashion, by any appropriate means such as an insulatingclamp or soldering for example, is a wafer-shaped piezoelectric element62 having the property of producing voltage differences between its topand bottom surfaces when mechanically stressed. Piezoelectric element 62may be of conventional type, comprising for example a wafer ofcrystalline barium titanate 62A having separate, mutually insulated,conductive contact layers 62B and 62C plated on its opposite majorsurfaces. The layer 62C is in electrical contact with block at. To thetop surface of piezoelectric element 62 beyond the supporting surface ofblock 6% there is affixed a body 64 of magnetic material which issusceptible of attraction by a magnet, and is typically of iron.Fastening of body 64 may be accomplished by conventional means, such ascementing, soldering, or mechanical crimping. In the preferredembodiment shown, the magnetic body 64 is generally U-shaped so as tofit over the top of element 62 and down opposite sides thereof, element62 being of a width such that the spacing between thedownwardly-extending sides of body 64 is substantially the same as thatbetween the poles of the fixed magnet presently to be described; it willbe understood that short-circuiting of electrodes 62B and 62C to eachother is prevented, for example by coating of the latter elements withan insulating cement 65.

Mounted on plate 59 directly beneath magnetic body 64 is a permanentmagnet of U-shaped cross section having its north and south poles spacedcircumferentially around plate 59 and extending upward towardpiezoelectric element 62. Preferably piezoelectric element 62 iscentered above the space between the magnet poles. Since body 64 is ofmagnetic material it is attracted downwardly by the magnetic field frommagnet 70, thus exerting a fiexure stress on piezoelectric element 62tending to bend downwardly its free end and to produce a voltage betweenconductive layers 62B and 62C. The magnitude of this force varies withthe strength of the magnetic field reaching body 64, and in accordancewith the invention this magnetic field is caused to vary as a functionof angular position of rotor shaft 35, as follows.

Attached in a plane normal to rotor shaft 35 and so as to rotatetherewith, is a generally circular field-modifying plate 80 of amagnetic material such as steel, vertically positioned on shaft 35 so asto move in rotation between magnet 70 and piezoelectric element 62without contacting either. Plate 80 is provided with a number ofperipheral apertures equal to the number of sparkplugs, in this casefour, circumferentially spaced from each other at 90 angular intervals.In the form shown the apertures are similar to each other, each having acircular portion, such as 82, of FIGURES 3 and 4 which may easily bepunched out from the plate 80, and a rectangular channel 84 extendingfrom the circular portion to the periphery of plate 80. The sides of thechannels are provided with downwardly-extending parallel flanges such as86 and 88, preferably spaced from each other by the distance between thepoles of magnet 70, and readily formed by cutting plate 80 adjacent eachcircular aperture and bending down the edges of each cut. The height ofthe flanges such as 86 and 88 is such as to clear the poles of magnet 70by a small margin upon rotation of plate 80.

In operation, as rotor shaft 35 turns, the magnetic field reachingmagnetic body 64 has a relatively small, reference value when the planeportion of plate 80 is interposed between it and magnet 70, due to thesubstantial spacing and the interposition of the continuous sheet ofmagnetic material of plate 80. However, when a rectangular aperture suchas 84 reaches magnet 70, the magnetic field at magnetic body 64increases, and reaches a maximum when a pair of flanges such as 86 and88 are aligned with the magnet poles as shown in FIGURE 4. In the lattercase the aligned flanges provide paths of low magnetic reluctance frommagnet 70 to the edges of the rectangular aperture in plate 80, and theabsence of magnetic material in the rectangular aperture and in theadjacent circular aperture permits strong fringing of magnetic fieldlines from magnet 70 upwards to magnetic body 64, increasing many-foldthe downward force on piezoelectric element 62 and causing it to beflexurally stressed and to generate a voltage change of predeterminedpolarity between its opposite contact layers 62B and 62C. The operationis therefore that of a flux gate. Stresses adequate to provide severalvolts of voltage change are readily produced with very small angulardeflections of piezoelectric element 62 of the order of a few microns sothat small spacings between plate 80 and element 62 may be used withoutdanger of physical contact between them. As plate 80 rotates farther,the magnetic field at body 64 decreases again to its small referencevalue, and the downward stress on piezoelectric element 62 is relievedso as to generate a voltage change of opposite polarity.

Accordingly, as each of the apertures in plate 80 passes in successionover magnet 79 a positive-going and a negative-going control voltagepulse are produced and delivered across cables 32 and 34 to operatecircuitry and produce a high-voltage pulse at cable 11. The times ofoccurrence of the control pulses are indicative of the attainment byrotor shaft 35 of specific predetermined angular positions. By locatingthe apertures in plate 80 angularly so that either the negative orpositive pulse occurs at a time such as to produce a high-voltage pulseat cable 11 when ignition of a spark plug is desired, the

necessary synchronization of ignition pulses with engine operation isobtained. For the present purposes I prefer to use a positive pulsegenerated when piezoelectric element 62 is downwardly flexed to cut offa normally-on transistor 46. Such operation is readily provided by oneskilled in the art by using well-known materials cut in known ways forthe piezoelectric element.

It is noted that there is no physical contact between thecontrol-voltagegenerating piezoelectric element 62 and the movingangular-position-indicating plate and no moving switch parts orhigh-current switch contacts are employed. Accordingly the system islong-lived, simple in construction, accurate even at very high enginespeeds, and compatible with the usual type of ignition-system equipmentcommonly employed.

From the foregoing it will be apparent that the invention is in no waylimited to the particular type of apparatus illustrated. Basically theinvention involves modifying the magnetic force acting on a magneticbody joined to a piezoelectric element, in accordance with the relativepositions of the body and an object whose position is to be indicated.For example, the magnetic material on the piezoelectric element may bemagnetized, permanent-magnet material, in which case the magnet ofFIGURE 2 may be, but is not necessarily, replaced by loW-retentivitymagnetic material. Alternatively the plate 81) may be replaced with anelement having discrete regions of strong permanent magnetization, as bylocating separate magnets in the positions occupied by the apertures inplate 80, in which case magnet 70 and plate 80 are unnecessary. In otherembodiments the relative motion may be provided by mounting one or morepiezoelectric elements for rotation past a fixed permanent magnet.Magnetic repulsion, rather than attraction, can be used in someinstances. Various geometric arrangements and types of relative motionmay also be employed to produce other types of stress of thepiezoelectric material, such as compressional or shear stress. Manyother diverse embodiments of my invention will occur to one skilled inthe art in view of the foregoing disclosure, and accordingly the scopeand spirit of the invention is to be limited only by the appendedclaims.

I claim:

1. Apparatus for producing position-indicating electrical variations,comprising:

a piezoelectric element; a body of magnetic material on said element;magnetic means, at least a part of which is of magnetic material andmovable relative tosaid body through positions adjacent but spaced fromsaid body, for producing different magnetic forces on said body fordifferent ones of said positions, thereby to produce stresses on saidelement and voltages therefrom indicative of the position of said partof said means with respect to said body; and motive means for movingsaid part relative to said body through said positions adjacent saidbody;

said magnetic means comprising an element for producing a magnetic fieldat said body and a member rotatable adjacent said body in response tosaid motive means for varying the strength of said magnetic field as afunction of the angular position of said member with respect to saidbody.

2. Apparatus in accordance with claim 1 in which said piezoelectricelement is mounted to flex in response to changes in said magneticfield.

3. Apparatus in accordance with claim 1, in which said element forproducing a magnetic field comprises a permanent magnet spaced from saidbody and in which said rotatable member has portions of differingmagnetic effect on said body, said portions being rotatable between saidbody and said permanent magnet.

4. Apparatus in accordance with claim 3, in which said rotatable membercomprises magnetic material defining at least one aperture therein andis disposed for rotation of said aperture through the region betweensaid body and said permanent magnet.

5. Apparatus in accordance with claim 4, in which said rotatable memberis of flux-gate form to increase the magnetic field at said body whensaid aperture is disposed between said body and said permanent magnet.

6. In an ignition system for a combustion engine of the class employinga shaft rotating in timed angular phase relation to the phase of theengine cycle, apparatus comprising:

a piezoelectric element responsive to changes in pressure thereon toproduce voltage pulses;

a magneic body connected to said piezoelectric element to exert on saidelement a pressure dependent upon the magnetic field strength at saidbody;

rotatable magnetic means having different portions of different magneticcharacteristics disposed circumferentially thereof, and angularlymovable relative to said magnetic body in timed relation to rotation ofsaid shaft to produce at said body a magnetic field varying inaccordance with angular position of said shaft, thereby to produce fromsaid piezoelectric element voltage pulses in predetermined timephaserelation to attainment by said shaft of predetermined angular positions;and

means for rotating said rotatable magnetic means in response to rotationof said shaft.

7. Apparatus in accordance with claim 6, comprising a permanent magnetspaced from said body and fixed with respect thereto, and in which saidmagnetic means comprises a magnetic member rotatable between saidpermanent magnet and said body.

8. In an ignition system for internal combustion engines comprising atleast one spark-ignition element for producing combustion in an enginecylinder, means responsive to electrical signals for developinghigh-voltage pulses for application to said spark-ignition element, anda shaft rotating in fixed time-phase relation to the operat ing phase ofsaid engine, the combination therewith of:

a piezoelectric element;

a magnetic body on said element;

a magnetic member connected to rotate adjacent said magnetic body insynchronism with said shaft to vary the magnetic force on said body andthe mechanical stresses on said piezoelectric element, thereby toproduce voltage pulses across said piezoelectric element in synchronismwith said shaft rotation, means for rotating said magnetic member inesponse to rotation of said shaft; and

means for supplying said voltage pulws to said means for developinghigh-voltage pulses, to control the time of generation of saidhigh-voltage pulses.

9. Apparatus in accordance with claim 8, comprising a high-voltagedistributor supplied with said high-voltage pulses and having a rotorconnector and a plurality of distributor contacts disposed to becontacted in sequence by said rotor connector upon rotation thereof, andin which said shaft is connected to rotate said rotor connector.

10. Apparatus for producing position-indicating electrical variations,comprising an elongated piezoelectric element mounted in a fixedposition at one end and having a first magnetic means attached thereonat the other end, second magnetic means including means movable relativeto said first magnetic means and through a series of discrete positionsadjacent to but spaced from the first magnetic means, said first andsecond magnetic means including means for imposing a mechanicalstressing force on said piezoelectric element at each of said positionsfor generating a voltage variation indicative of the position of saidmovable means, and motive means mechanically connected to said movablemeans for moving the same in sequence through said positions.

References Cited by the Examiner UNITED STATES PATENTS 2,683,856 7/1954Kornei 3222 2,827,531 3/1958 OBrien 20()87.3 2,875,353 2/1959 Cavalieriet al. 3108.5 2,954,506 9/1960 Harkness 315-209 JOHN W. HUCKERT, PrimaryExaminer.

JAMES D. KALLAIH, DAVID J. GALVIN, Examiners.

1. APPARATUS FOR PRODUCING POSITION-INDICATING ELECTRICAL VARIATIONS, COMPRISING: A PIEZOELECTRIC ELEMENT; A BODY OF MAGNETIC MATERIAL ON SAID ELEMENT; MAGNETIC MEANS, AT LEAST A PART OF WHICH IS OF MAGNETIC MATERIAL AND MOVABLE RELATIVE TO SAID BODY THROUGH POSITIONS ADJACENT BUT SPACED FROM SAID BODY, FOR PRODUCING DIFFERENT MAGNETIC FORCES ON SAID BODY FOR DIFFERENT ONES OF SAID POSITIONS, THEREBY TO PRODUCE STRESSES ON SAID ELEMENT AND VOLTAGES THEREFROM INDICATIVE OF THE POSITION OF SAID PART OF SAID MEANS WITH RESPECT TO SAID BODY; AND MOTIVE MEANS FOR MOVING SAID PART RELATIVE TO SAID BODY THROUGH SAID POSITIONS ADJACENT SAID BODY; SAID MAGNETIC MEANS COMPRISING AN ELEMENT FOR PRODUCING A MAGNETIC FIELD AT SAID BODY AND A MEMBER ROTATABLE ADJACENT SAID BODY IN RESPONSE TO SAID MOTIVE MEANS FOR VARYING THE STRENGTH OF SAID MAGNETIC FIELD AS A FUNCTION OF THE ANGULAR POSITION OF SAID MEMBER WITH RESPECT TO SAID BODY. 